1. Field of the Invention
The present invention relates to an ultra-precision positioning technique and, more particularly, to a high-speed, high-precision positioning apparatus which is required to have, for example, a positioning resolution on the submicron order or less. The present invention also relates to an information recording/reproducing apparatus and inspection apparatus which are used in the semiconductor manufacturing industry and the fields associated with the manufacture of high-density recording media such as hard disks and information write/read operation.
2. Related Background Art
FIG. 8 shows a conventional direct-acting positioning apparatus.
An object (not shown) is mounted on a table 521. The table 521 can move in the X direction. A gravity guide 523 supports the table 521 on a horizontal X-Y reference surface in the gravity direction (Z direction). A yaw guide 522 has an X-Z guide surface perpendicular to the X-Y reference surface of the gravity guide 523 and parallel to the moving direction of the table 521, and supports the table 521 in the Y direction. That is, the table 521 is moved in the X direction by "two-surface restraint guiding" by means of the gravity guide 523 and yaw guide 522.
A feed screw driving unit 524 drives the table 521 in the X direction in a noncontact state by converting the rotating motion transferred from a motor into a translating motion. The feed screw driving unit 524 has a motor and feed screw which are substantially integrated with the gravity guide 523, and a nut (not shown) integrated with the table 521 to convert a rotating motion into a translating motion.
An optical encoder 525 measures the position of the table 521 in the X direction. A head is fixed on the yaw guide 522. The encoder 525 measures the position of the table 521 in the X direction at a position near the yaw guide 522. The driving amount of the feed screw driving unit 524 is feedback-controlled by using the position information about the table 521 which is measured by the encoder 525, thereby positioning the table 521.
FIG. 9 shows a model indicating a positional relationship when the conventional stage unit is viewed from the Z direction.
The table 521 has a barycentric position 531. At a yawing restraining position 532, the table 521 is supported by the guide surface of the yaw guide 522 to be restrained in the yawing direction. At a driving position 534, the table 521 is driven by a thrust F from the feed screw driving unit 524. At a measuring position 535, the encoder 525 measures the position of the table 521.
As shown in FIG. 9, the driving position 534 of the thrust F from the feed screw driving unit 524 is set to pass through the barycentric position 531 of the table 521.
In addition, as shown in FIG. 9, the measuring position 535 at which the position of the table 521 is measured is relatively near the yawing restraining position 532. By setting the measuring position 535 near the yawing restraining position 532, even if the table 521 undergoes posture variations in the yawing direction, a disturbance due to the yawing posture variations is prevented from affecting measurement of the position of the table 521 in the translating direction.
In a positioning apparatus for driving a motor by feeding back the position of a table, the transfer function of a system has a great influence on the positioning time and the stability of a feedback system. When, for example, the gain of a feedback loop compensator is increased, hunting occurs in the worst case. If the gain is set low to improve the stability of the system, a necessary steady-state precision cannot be ensured. In addition, if a rotation/translation conversion element such as a feed screw driving unit is inserted in the system, nonlinearity such as hysteresis or lost motion occurs. As a result, a phase delay occurs in the transfer function, and the responsivity deteriorates.